Hi Brooke, Metric screws are spec'd by major diameter, and the number of mm between the peaks of the threads. English are spec'd by diameter, and the number of threads per inch.
A 40TPI screw corresponds to a (1/40) * 25.4 = 0.635 mm pitch. There are standard metric pitches of 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, and 1.0 mm. What you are seeing is probably an M3-0.5, M3-0.6, or an M4-0.7 screw. -Chuck Harris Brooke Clarke wrote: > Hi: > > There was a recent incident when a passenger aircraft (maybe Canada) had > to make an emergency landing because of a wrong metric - English > conversion resulted in not enough fuel to get to the destination. > > Are there metric equivalents to different series of English threads. > For example I recently purchased a tap for 8-40 threads after mistakenly > purchasing a 6-40 tap. Most good hardware stores in the US have 4-40 > taps, dies, various lengths screws and nuts. Although 6-40 and 8-40 are > standard sizes they are not commonly stocked. Are there a a number of > alternative combinations of root diameter and pitch in the metric system? > > Have Fun, > > Brooke Clarke _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
